The present invention relates generally to surface emitting lasers, and more particularly to an improved vertical microcavity surface emitting laser diode structure.
Vertical-microcavity surface-emitting laser diodes (microlasers), as single devices or in one or two dimensional arrays, are candidate replacements for vertical-cavity surface-emitting lasers (VCSELs) in various low to moderate power applications such as optical interconnects, datalinks, and printing, display and spectroscopic sensor devices, because the microlaser offers improved threshold current and more stable single (fundamental) mode lasing.
A microlaser is similar to a VCSEL except that the microlaser optical cavity dimensions are all on the order of the emission wavelength. The length of the optical cavity along the resonant direction (normal to the planar layer interfaces, nominally the z direction in Cartesian coordinates) is roughly one-half of the emission wavelength. The width of the cavity (in the x and y directions) is approximately less than five times the emission wavelength. In contrast, although a VCSEL cavity may have the same length as a microlaser, the width of the VCSEL cavity is at least five times the emission wavelength and generally much greater than this.
Prior art laser diode devices have not provided for microlaser resonant emission wavelength blueshifting, i.e. shifting to shorter wavelength, for transverse microlaser dimensions equal to or less than the peak emission wavelength. The resonant cavity of the prior art devices along the axial (z) direction must therefore be carefully sized in order to minimize the threshold current density. Conventional laboratory VCSELs have threshold currents below one milliampere. Microlasers offer further reduction in threshold current due to their smaller active area and increased spontaneous emission coupling into the resonant lasing mode. Measurement of peak emission wavelength can be used as a quality/processing control step in the large-scale manufacturing of microlasers since it can be related to the success of an oxidation processing step.
A potential drawback of microlasers is multimode lasing. Traditionally, this occurs when the threshold gain of several transverse laser modes is comparable and more than one mode can acquire sufficient gain to lase. However, with ajudicious selection of gain material, this potential problem can be overcome. In accordance with a principal feature of the invention, if the gain spectrum is sufficiently narrow--as is possible in quantum dots--only the fundamental mode may lase. According to the invention, the spectral separation between the fundamental and higher order lasing modes, due to the difference in the mode blueshifts, is exploited to achieve single mode lasing.
It is therefore a principal object of the invention to provide an improved microcavity surface-emitting laser.
It is a further object of the invention to provide an intracavity waveguiding structure for a microcavity surface-emitting laser.
It is yet another object of the invention to provide a microcavity surface-emitting laser having a three-dimensional waveguiding structure using native aluminum oxide layers.
It is yet another object of the invention to provide an improved microlaser, which corrects for emission wavelength blueshift caused by reduced lateral waveguiding geometry of the structure.
It is yet a further object of the invention to provide a microlaser structure having improved side mode suppression through spectral separation of the fundamental and higher-order lasing modes.
These and other objects of the invention will become apparent as a detailed description of representative embodiments proceeds.